1. Field of the Invention
The present invention relates generally to backlighting systems for use in displays such as liquid crystal displays.
2. Description of the Related Art
An exemplary application of backlighting is its use in the display of portable electronic devices such as notebook computers, laptop computers, digital cameras, and cell phones. The displays of these devices are generally formed by positioning an array of liquid crystals between a light source and a viewer. Essentially, each of the liquid crystals then act as a variable shutter which passes a selected portion of the light from the light source to the viewer. Each liquid crystal forms one pixel of the display image and command signals to the liquid crystals can then command the generation of various images on the display. Brightness of the display can be controlled via control of the light source.
One light source embodiment for backlighting uses at least one cold-cathode fluorescent lamp (CCFL). CCFLs can be mounted along the edge of the liquid crystals or can be spaced uniformly over the back of the liquid crystals. A more recent light source embodiment for backlighting is formed with multiple light-emitting diodes (LEDs). The number of LEDs required varies with the size of the display. For example, laptop computer displays generally use between 42 and 72 LEDs. The number of LEDs may easily exceed a hundred in other applications. Use of LEDs for the backlighting light source provides a number of advantages which include reduced size, weight, and power, increased brightness, enhanced colors, greater lifespan and elimination of the use of mercury. Although LEDs typically provide a white backlight, they can also be configured to provide other backlight colors.
Calibration of the LED currents is desirable to insure that the backlighting is uniform and thereby pleasing to the eye of an observer. This calibration has typically been accomplished via use of specialized calibration systems formed, for example, with automatic test equipment, arrays of fuses and interface structures.